The present invention relates generally to a processor for processing replies received by a secondary surveillance radar system. More particularly, the present invention relates to a processor that employs a processing method designed to reduce the occurrence of multiple target reports from a single physical target.
Secondary Surveillance Radars (SSR) presently in use employ interrogator transmitters, which query transponders aboard civilian and military aircraft, civilian and military ships, and other ground, airborne or sea based platforms. For purposes of this discussion, we will refer to an aircraft as the transponder platform. The interrogators are generally associated with a reply receiver, quantizer, reply decoder, and reply processor that together process replies received from the transponders aboard the aforementioned aircraft. These replies contain information that among other things convey the identity of the aircraft, the altitude of the aircraft and other information. The transponder information transmitted is based upon the interrogation mode the SSR employs at a given time.
The reply processor operates to create what are known as target reports. Target reports are then used xe2x80x9cdownstreamxe2x80x9d for further processing such as by trackers, displays, or other data reduction devices. Unfortunately, at times, processing a set of returned replies from a single target can result in the creation and output of multiple target reports associated with the single target. These multiple target reports associated with a single target result in post-processing errors by the trackers, displays, and other data reduction devices. For example, in the case of a display, if two target reports are generated for the same target, then the display visually indicates the presence of two targets or objects in the same spatial area. As one can appreciate, two objects appearing in the same spatial area can be problematic, particularly in the area of air traffic control. The creation of multiple target reports for a single object target is exacerbated when two or more interrogation modes (to be discussed in more detail below) are interlaced within a single scan of the interrogator, an approach that is fairly common.
Prior attempts to solve the creation of multiple target reports have had limited success. Solutions have included post-processing the target reports prior to use by the trackers, displays or other data reduction devices in an effort to identify occurrences of multiple target reports. For example, attempts have been made to process the target reports created by the interrogator in order to eliminate or ignore one or more of the multiple target reports. Although somewhat effective, this post-processing of target reports suffers from drawbacks. For example, the post-processing can be time consuming, which can impact negatively the performance in time critical situations of the SSR. Additionally, the quality of the reports that are passed to the tracker, display or other data reduction device may be degraded as a result of the post-processing of the target reports.
Other solutions to this problem have focused on the correlation and association of the reply data the SSR receives from the transponder that is performed within the interrogator. Attempts have been made to correlate and associate replies from multiple modes during an integrated target report building process. In other words, the interrogator attempts to correlate and associate the received reply data to a target regardless of the interrogator mode to which the transponder sent the data in reply. This integrated target report building process can result in situations where the reply data for one mode is correctly correlated and associated to the target but the reply data in a second mode is incorrectly correlated and associated to that same target.
Therefore, it would be advantageous to have a Secondary Surveillance Radar system that minimized the occurrence of multiple target reports for a single target. In particular, it would be advantageous to have a Secondary Surveillance Radar system that did not require post-processing of created target reports before the target reports are provided to trackers, displays, or other data reduction devices. It would also be advantageous to have a Secondary Surveillance Radar system that distinguished between reply data received from a single target in response to different interrogation modes utilized by the interrogator of the system.
In accordance with one aspect of the present invention is provided a method of processing reply signals received in response to an interrogation by a secondary surveillance radar system. The method includes the steps of receiving a reply signal from each of a plurality of targets, and enabling each of a plurality of existing target mode blocks having a predefined mode to select from the reply signals. The method further includes the step of correlating the selected reply signal to the target mode block that selected same.
In accordance with another aspect of the present invention is provided a method of processing reply signals received in response to an interrogation by a secondary surveillance radar system that includes the step of receiving a reply signal from each of a plurality of targets. The method further includes the steps of correlating the reply signals to one of a plurality of existing target mode blocks, selecting the existing target mode blocks that satisfy a predetermined mode declaration criteria, and identifying the selected existing target mode blocks to be used to build a plurality of target reports.
In accordance with still a further aspect of the present invention is provided a secondary surveillance radar system for sending a plurality of interrogations and receiving a plurality of reply signals in response thereto. The system includes a transmitter for sending the interrogations, and a receiver having an output for receiving the reply signals. The system further includes a processor operatively coupled to the output for processing the reply signals. The processor has a memory for storing a plurality of existing target mode blocks, and a first correlator for selectively correlating the reply signals to one of the plurality of existing target mode blocks. In addition, the processor has a means for establishing a dynamic predetermined mode declaration criteria, and a second correlator for selectively correlating the target mode blocks that satisfy the predetermined mode declaration criteria to one of a plurality of existing target reports.
In accordance with still another aspect of the present invention is provided a secondary surveillance radar system in which a means for establishing a dynamic mode declaration criteria calculates with respect to a plurality of target mode blocks an average number of correlations per interrogations expressed as an average percentage.